Projections by the Energy Information Agency and current Intergovernmental Panel on Climate Change (IPCC) expect worldwide electric power demand to double from its current level of about 2 terawatts electrical power (TWe) to 4 TWe by 2030, possibly reaching 8-10 TWe by 2100. They also expect that for the next 30 to 50 years, the bulk of the demand of electricity production will be provided by fossil fuels, typically coal and natural gas. Coal supplies 41% of the world's electric energy today, and is expected to supply 45% by 2030. In addition, the recent report from the IPCC has placed the likelihood that man-made sources of CO2 emissions into the atmosphere are having a significant effect on the climate of planet earth at 90%. “Business as usual” baseline scenarios show that CO2 emissions could be almost two and a half times the current level by 2050. More than ever before, new technologies and alternative sources of energy are essential to meet the increasing energy demand in both the developed and the developing worlds, while attempting to stabilize and reduce the concentration of CO2 and other greenhouse gases in the atmosphere, and mitigate the concomitant climate change.
Nuclear energy, a non-greenhouse-gas emitting energy source, has been a key component of the world's energy production since the 1950's, and accounts for about 16% of the world's electricity production, a fraction that could—in principle—be increased. Several factors, however, make its long-term sustainability difficult. These concerns include the risk of proliferation of nuclear materials and technologies resulting from the nuclear fuel cycle; the generation of long-lived radioactive nuclear waste requiring burial in deep geological repositories; the current reliance on the once-through nuclear fuel cycle; and the availability of low-cost, low-CO2-footprint uranium ore. In the United States alone, nuclear reactors have already generated more than 55,000 metric tons (MT) of spent nuclear fuel (SNF). In the near future, the US will have enough spent nuclear fuel to fill the proposed Yucca Mountain geological waste repository to its legislated limit of 70,000 MT.
Fusion is an attractive energy option for future power generation, with two main approaches to fusion power plants now being developed. In a first approach, Inertial Confinement Fusion (ICF) uses lasers, heavy ion beams, shock ignition, impulse ignition, pulsed power, or other techniques to rapidly compress capsules containing a mixture of isotopes of hydrogen, typically, deuterium (D) and tritium (T). As the capsule radius decreases and the DT gas density and temperature increase, DT fusion reactions are initiated in a small spot in the center of the compressed capsule. These DT fusion reactions generate both alpha particles and 14.1 MeV neutrons. A fusion burn front propagates from the spot, generating significant energy gain. A second approach, Magnetic Fusion Energy (MFE) uses powerful magnetic fields to confine a DT plasma and to generate the conditions required to sustain a burning plasma and generate energy gain.
Important technology for inertial confinement fusion is being developed at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in Livermore, Calif. At LLNL, a laser-based inertial confinement fusion project designed to achieve thermonuclear fusion ignition and burn uses laser energies of 1 to 1.3 MJ. Fusion yields of the order of 10 to 20 MJ are expected. Fusion yields in excess of 200 MJ could be expected to be required in central-hot-spot fusion geometry if fusion technology, by itself, were to be used for cost-effective power generation. In order to reduce the demands on the magnitude of the fusion yield required for economically viable power generation, it should be possible to couple a fusion system to a fission system, creating a so-called “hybrid” engine. Such a system would use the neutrons produced by fusion to cause transmutation or fission of fertile or fissile nuclei in a region exposed to the fusion neutrons. The energy released by the fission reactions then multiplies the energy released by the fusion reactions, thereby achieving an overall level of power production (fusion+fission) that is economically viable.
LLNL has been studying a fusion system, the Laser Inertial-confinement Fusion Energy (LIFE) engine that could be the fusion portion of a hybrid energy system. It is possible that hybrid LIFE power plants could be introduced into the U.S. economy before 2030. At present, the U.S. supply of depleted uranium (DU) is approximately 550,000 tons. If burned in hybrid LIFE systems as described herein, this would generate approximately 550 TWe-yrs of power. If estimates that the total U.S. electricity demand could reach about 2 TWe by 2100 are accurate, the current stockpile of DU alone could supply the total U.S. electric demand for nearly 300 years. In addition, a significant advantage afforded by the combination of fusion and fission, is that a hybrid LIFE system could potentially burn existing and future inventories of spent nuclear fuel (SNF) from light water reactors (LWRs). At present, in the U.S. alone, the current inventory of SNF in temporary storage at reactor sites is roughly 55,000 MT.
In addition to the U.S. scenarios described above, LIFE technology offers an attractive pathway for the expansion of nuclear power around the world. Proliferation concerns are mitigated compared to other nuclear technologies, and nuclear fuel for hybrid LIFE systems is inexpensive and widely available. Moreover, because a hybrid LIFE system employs a self-contained, closed fuel cycle, and it burns its fuel to the point where the actinide content of the spent fuel is less than 1% of its original content, nuclear waste repository considerations are simplified, particularly for countries not willing to build such underground repositories.
The hybrid fission-fusion engines described above can use either solid fuels or molten salt fuels for the fission portion of the system. The potential use of molten salts as fuels for the hybrid LIFE system, however, places certain demands on the melting temperature of the fuel, the nuclear properties of the fuel, the chemical stability of the fuel, the solubility of fissile and fertile materials in the fuel, and compatibility of the fuel with structural materials. Thus, there is a need in the art for improved molten salt fuels suitable for use in the hybrid LIFE systems. Surprisingly, the present invention meets these and other needs.